Stainless steels represent a good alternative for the construction of all types of equipment, because they are resistant to homogenous corrosion under controlled conditions in many industrial application types, in household appliances, kitchen utensils, for decorative goals, in architecture etc. However, a problem which faces these types of materials is corrosion, such as when used under inappropriate conditions, for example, high temperatures, marine environments, etc. This is what constitutes the system: “material and its environmental surroundings”. When the material and its surroundings react chemically, a change occurs in its nature which, generally, leads to deterioration of its design properties or of its physical characteristics. As a consequence of exposure to inadequate conditions, the materials with which household appliances are manufactured with are subject to crusting (dirtying) with oils and grease originating from the heating of foods. These problems are some of the more common ones in the metal and ceramic cooking utensils, which decrease their value and effective life use.
Temperatures above 200° C. are another factor which affects the appearance of stainless steel, which is reflected with the formation, and increase in the thickness of the chrome oxide layer, which at a simple glance, is seen as a change of color on the surface with a tendency to yellowing. This color change on the surface of a household appliance alerts the user to the fact that his appliance has become dirty, in addition to the grease accumulation encrusted onto the steel surface, and to attempt to get rid of the layer which has formed, a variety of chemical products are used, causing the household appliance appearance to deteriorate, thus causing the user to choose to switch his household appliance and this entails dissatisfaction.
The easy clean coatings applied on glass and other inorganic surfaces have garnered a lot of attention in recent years. Among the main advantages of these materials which have been treated with easy clean films, it has been found that the dirtiness is easily removed given the side effect created by a low energy surface (such as, for example, oleo-phobic, lipo-phobic or hydrophobic) and the more aggressive cleaning agents thus become unnecessary; which makes these coatings highly attractive for applications onto kitchen utensils, household appliances and all appliances exposed to foods, greases and edible oils subjected to continuous use conditions and to temperature cycles (room temperature −350° C.). However, several disadvantages exist with the commercial products which are used to produce coatings over the stainless steel covers, among others are that some of the formulations contain solvents which are health toxic and noxious to the environment, such, as, for example, petroleum and halogenated hydrocarbons, which are not acceptable for the above mentioned applications. There are also those which create coatings with low resistance to abrasion, which translates into materials with short effective life use.
Currently, among the main general characteristics which the easy clean coatings should possess in order to be widely accepted are: water repellence, grease repellence, oil repellence, temperature resistance, abrasion resistance, stability to ultraviolet light and to the cleaning agent products, it should be easily applied in addition to being transparent and non-toxic.
A wide variety of easy clean coatings have been developed, among which we should mention those revealed in the following patent literature:
Publication WO2008/0517879 A1 (Moses, et al, 2008), describes a method for forming an easy to clean coating on a metallic or metalized substrate, by means of a layer formed of silicon, oxygen and hydrogen and at least one part deposited by means of the PD method (plasma-deposited) and one part of a fluoridated compound.
U.S. Pat. No. 4,792,358 (Kimura, at al., 1988) refers to a composition of an inorganic coating which has 100 parts in solid weight with a thermally prepared agglutinant with 10 to 40 weight parts in fine silicon particles in approximately 100 parts in solid weight of potassium silicate and 15 parts in weight of 100 parts of pigment set in mother of pearl in order to create shine.
U.S. Pat. No. 7,683,293 B2 (Buzzi, et al, 2010), presents a protective coating, transparent and high-temperature resistant for use in household appliances, particularly those cooking appliances with metallic surfaces. This coating is deposited on the metallic surfaces by means of Plasma-enhanced chemical vapor deposition (PECVD), which itself incorporates at least one layer of SiO2 and one intermediate layer of SiC. This coating protects the metallic surface is resistant to scratching, soiling and to yellowing due to heating. The method of application of the coating discussed in this invention is by means of Plasma-enhanced chemical vapor deposition of the precursors, which are vaporized to later interact and form chains between them, all of this is undergone in a vacuum deposition chamber and under the action of the plasma.
Chinese patent application No. 1978563 A (Changguo, Huang, 2006), which consists of a re-coating formed by inorganic titanates. The coating precursor is an aqueous suspension containing titanates (M(II2TiO4), meta titanates (M(II)TiO3) and titanate mixtures (M(I)2Ti2O5); where M refers to the alkaline metals: potassium, lithium and sodium, earth metal alkalines such as, for example, barium, strontium, magnesium and calcium, as well as zinc, iron and aluminum. The re-coating does not contain chrome nor does it present water-absorption problems or softness.
Chinese Patent application No. 101462859 A (Ye, et al., 2009) is related to a re-coating which reduces the stainless steel oxidation in a high temperature oven. The re-coating is composed of silicon oxide, aluminum oxide, magnesium oxide, calcium oxide and boric oxide.
European Patent application number EP 2 034 050 A1 presents as the main objective the providing of a re-coating for steel whose properties are resistance to detachment, resistance to solvents, resistance to the alkali, in addition to an increase in abrasion resistance. This re-coating is a compound material which consists of a resin, polyurethane resin nano-particles and of the copolymerization of carboxylic acid and unsaturated ethylene, a substance with a silanol group and/or alcoxysilane, non-particulate silicon oxide, a titanium organic compound and polyolefin wax particles. In addition to these compounds, the invention recommends adding an agent which can prevent oxidizing, selected among a group of phosphate compounds, thiocarbonyl compounds, niobium oxide and guanidine compounds.
Other documents related to re-coatings are the following: EP 2 037 003 A1, GB 1 471 977 A, JP 63 291 665, RU 2 203 233, U.S. Pat. No. 5,466,280 A, US 2004/03796 A1, ES 2 252 804 13, GB 2 425 976 A, JP 2004/050772, U.S. Pat. No. 4,071,380 A, U.S. Pat. No. 5,554,681 A, US 2005/208272 A1, GB 1 189 823 A, JP 11 349 852, KR 100 782 640, U.S. Pat. No. 5,147,730 A, U.S. Pat. No. 7,488,515 B2, WO 01/46324 A2.
Notwithstanding the wide variety of available re-coatings in the state of the art, there still exists the need to develop new re-coatings which can be used on metallic surfaces, preferably for application onto household appliances with metallic surfaces, which avoid the yellowing of the surface, aid in the cleaning of the same and additionally develop less expensive methods, with easy application, which enable the preparation as well as the application of the coatings.
Advantageously, the coating of the present invention allows the user to accomplish the cleaning of the coated surfaces of the household appliance using solely a sponge or a wet rag, thereby avoiding the use of abrasive products which might damage the metallic surface and thus maintaining the product's appearance for a longer time period.